1. Field of the Invention
The present invention relates to the control of fuel burning devices in general and in particular relates to a fuel oil burner operating with intermittent ignition and using a hot surface 120 volt ignitor electrode that is sintered to full density with no porosity and that will withstand applied voltages in excess of 230 volts AC for short duty cycles, a circuit for controlling the duty cycle, and a voltage phase regulator circuit to operate an 85 to 120 volt hot surface ignitor from a 180 to 254 volt AC source or operate a 60 volt hot surface ignitor from a 60 to 132 volt AC source and providing half wave consistent output voltage to the ignitor and that further includes a trial ignition period during which time a blower motor of the split-phase type, and having a main winding and an auxiliary start winding, provides both air and fuel to the combustion chamber. If a flame is not detected in less than one second, the device is de-energized and starting must be retried.
In a second embodiment, a series-type voltage regulator circuit is used to operate an 85 to 120 volt hot surface ignitor from a 180 to 254 volt AC source, to operate a 60 volt hot surface ignitor from a 60 to 132 volt AC source, or to operate an 85 volt hot surface ignitor from an 85 to 132 volt AC source and providing full wave consistent output voltage to the ignitor.
In the third embodiment of the present invention, a first circuit is provided that applies full-wave voltage to the ignitor only during the preheat and ignition trial periods for ignition purposes. A second circuit is provided that applies half-wave voltage to the ignitor continuously, beginning with the RUN period, for fast re-ignition and to burn any fuel coming in contact with the ignitor during the RUN period and thus prevents carbon buildup on the ignitor, especially if heavy fuels, such as diesel, are used. A third circuit is provided which automatically adjusts the preheat time and the ignition on-time, depending on the applied line voltage and the current draw of the ignitor.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Portable forced air kerosene heaters typically comprise an outer housing surrounding a combustion chamber. Air is forced into the combustion chamber. A burner is located at one end of the combustion chamber and the burner normally has a fuel nozzle frequently incorporating eductor means providing jets of air to draw, mix, and atomize the fuel delivered by the nozzle. The nozzle, together with the eductors, discharges a combustible fuel-air mixture into the combustion chamber. An ignitor is provided to ignite the mixture and, after initial ignition, continuous burning occurs. Typically, during the continuous combustion, forced air heat currents issue from the end of the heater opposite the burner and additional heat radiates from the surface of the heater housing.
Portable space heaters of the general type described are frequently provided with a direct spark type of ignitor and a motor. The motor normally runs a fan supplying air to the combustion chamber and the eductors and operates a fuel pump or air compressor to supply the fuel to the combustion chamber.
When the portable space heater is functioning properly, fuel burning will occur near the end of the combustion chamber at which the burner is located. In the event of reduced air flow, however, the flame will move toward the opposite end of the combustion chamber, the oxygen supply becoming inadequate for proper combustion. Under such a circumstance, it is desirable to shut down the heater. Inadequate air may result because of a malfunction of the fan or a blocking of the passages for air into or out of the combustion chamber.
It is also desirable to shut down the portable space heater when there is a flame failure. This can occur by virtue of faulty ignition, a blockage of the fuel nozzle, or exhaustion of the fuel supply.
Further, the prior art portable heaters utilize a spark gap for ignition. Some use heating coils that glow at a particular temperature sufficiently hot to cause ignition.
Hot surface ignition systems (HSI) have been used for more than twenty years for gas ignition in units such as gas clothes dryers, gas ovens, gas fired furnaces, and boilers thus replacing and eliminating standing gas pilot lights. Low voltage ignitors (12 and 24 volts) of the hot surface type are made from a patented ceramic/intermetallic material. These ignitors are used in compact low wattage assemblies for ignition of gas fuels. The element reaches ignition temperature in less than 10 to 15 seconds and utilizes about 40 watts of power. The ignitor is made from a composite of strong oxidation resistant ceramic and a refractory intermetallic. Thus hot surface ignitors have no flame or spark. They simply heat to the required temperature for igniting a fuel air mixture. Such ignitors have not been used in oil burning systems because the ignitor material is porous and oil entering the porous cavities causes buildup of the materials that are inimical to the operation of the burner.
A 120 V HSI ignitor has been developed in which the material is compressed and sintered to full density leaving no porosity resulting in a high performance ceramic composite. It can operate at very high temperatures such as 1,300 to 1,600 degrees Celsius. This same ignitor can withstand 230-volt operation at a reduced duty cycle to prevent overheating. The application of such high voltage hot surface ignition device is especially attractive for use in the present invention wherein fuel oil burning heaters are to be constructed. They provide unique advantages over prior art gas flames, heating coils, and spark gap ignition systems. However, the temperature of said hot surface ignitor varies with the applied voltage and some variation is found in normal response variations among the ignitors themselves.
This invention solves this problem by providing a circuit that responds to both current and voltage applied to the hot surface ignitor and is also used to operate a 120-volt ignitor directly on 230 volts or operate a 60-volt hot surface ignitor from a 60 to 132 volts AC source without a step-down transformer or series connected power dissipating devices.
In any case, malfunctions in the prior art heaters can cause insufficient or incomplete burning or a failure to burn issuing fuel thus producing a dangerous condition of highly flammable liquid or noxious fumes. Prior art devices include a number of safety control circuits for fuel burning devices that are proposed to avoid the many and often undesirable results of improper burning or flame failure.
Thus, in U.S. Pat. No. 3,713,766 (Donnelly oil burner control 1973), a pretrial ignition period is determined by a bimetallic thermal switch which, after a predetermined period of time if ignition has not started, opens and removes the power to the heater.
Manual resetting of the bimetallic contacts is required to restart. However, during burner operation, if the flame for any reason goes out, a new trial period is automatically reinitiated. This could be dangerous if a fuel buildup in the combustion chamber is ignited. Further, if the photocell detecting the flame is shorted during operation, the burner will continue to operate because the circuit cannot detect that the photocell has been shorted and a shorted photocell condition is similar to the normal flame condition, which is a very low photocell resistance. The control will only detect a shorted photocell at start-up. Further, spark ignition is constantly applied during each cycle of the line voltage. Finally, there is an electric spark ignition circuit. Further, this control does not provide a motor start drive or preregulator or voltage regulator power supply circuits. In addition, this control does not provide current or voltage regulation to the ignitor.
In U.S. Pat. No. 3,651,327 (Thomson oil burner control 1972), a fluctuating control signal, due to flame fluctuation, is rectified and energizes a relay. This circuit is entirely a DC circuit. It responds only to the presence or absence of a flame and would require a separate circuit for a trial ignition period. It has no start-up circuit or restart circuit, no preheat circuit, and no hot surface ignition. Again, this control does not provide a motor start drive or preregulator or voltage regulator power supply circuits and, further, this control does not provide current or voltage regulation to the ignitor.
In U.S. Pat. No. 3,672,811 (Horon oil burner control 1972), if the photocell shorts during operation, there is no detection of loss of flame. Thus there is no shutdown of the fuel flow to the burner or the air blower. It also uses a spark gap ignition with a continuous spark being applied. There is no hot surface ignition and it does not provide a motor start drive or preregulator or voltage regulator power supply circuits. It also does not provide current or voltage regulation to the ignitor.
In U.S. Pat. No. 3,741,709 (Clark, commonly assigned), if the unit fails to start during an ignition trial period, a resistance heater opens the contacts of a thermal breaker unit to remove power. There is no shutdown of the control system if the photocell shorts. This control does not provide an ignition preheat period required for HSI ignition. This control does not provide an ignition preheat period required for HSI ignition. This control does not have the separate ignition control circuit for intermittent ignition. However, this control does contain moving parts. The timings of this control vary greatly with a change in applied voltage. There is no HSI ignition and, again, this control does not provide a motor start drive or preregulator or voltage regulator power supply circuits. This control also does not provide current or voltage regulation to the ignitor.
In U.S. Pat. No. 3,393,039 (Eldridge Jr. gas burner), if the unit fails to start during an ignition trial period, a resistance heater opens the contacts of a thermal breaker unit to remove power. It utilizes only AC voltage, uses a mechanical relay to cause continued operation of the circuit by detecting the heat of the flames, and has an automatic restart. It is not shut down during operation if the flame is gone. It simply keeps trying to ignite the fuel. Further, there is no hot surface ignition and the control does not provide a motor start drive or preregulator or voltage regulator power supply circuits, neither does it provide current or voltage regulation to the ignitor.
In U.S. Pat. No. 3,537,804 (Walbridge), an ignitor coil is used rather than a spark gap or pilot flame for ignition. The temperature of the ignitor coil is sensed by a photocell and, when the proper temperature is reached, the fuel valve is opened. It has a trial ignition in which, if a flame does not occur, a heating element opens bimetallic contacts to remove power. If the photocell is shorted during operation, the system simply tries to restart and does not shut down unless the heating element in the circuit reaches a predetermined temperature. Again, this device does not provide a motor start drive or preregulator or voltage regulator power supply circuits and neither does it provide current or voltage regulation to the ignitor.